Several facets of placental lactogen physiology will be examined in the mouse. Mouse placental lactogen will be isolated and purified from placentae of mice in late gestation, and an antiserum to the hormone will be generated. A homologous radioimmunoassay for mouse placental lactogen will be developed. The antiserum, and one previously generated to mouse pituitary prolactin, will be used to examine the relative quantitative significance of these hormones to functional mammary gland development and to maintenance of progesterone secretion by the ovary during pregnancy. In addition, the regulation of mouse placental lactogen secretion will be examined on several days of gestation both in vitro and in vivo. The site of production of mouse placental lactogen in the placenta will be determined.